Various inkjet printing arrangements are known in the art and include both thermally actuated printheads and mechanically actuated printheads. Thermal actuated printheads tend to use resistive elements or the like to achieve ink expulsion, while mechanically actuated printheads tend to use piezoelectric transducers or the like.
A representative thermal inkjet printhead has a plurality of thin film resistors provided on a semiconductor substrate. An orifice and/or a barrier layer is provided on the substrate. The orifice and/or the barrier layer defines firing chambers about each of the resistors, an orifice corresponding to each resistor, and an entrance to each firing chamber. Actuation of a heater resistor by a “fire signal” causes ink in the corresponding firing chamber to be heated and expelled through the corresponding orifice.
Ink typically is provided at the entrance of the firing chamber through a feed slot that is machined in the semiconductor substrate. The substrate usually has a rectangular shape, with the slot disposed longitudinally therein. Resistors are often arranged in rows located on one or both sides of the slot. The width of the print swath achieved by one pass of a printhead is approximately equal to the length of the resistor rows, which in turn is approximately equal to the length of the slot.
Feed slots have typically been formed by sand drilling (also known as sandblasting or “sand slotting”). This method is a rapid, relatively simple and scalable process. The sand blasting method is capable of forming an opening in a substrate with a relatively high degree of accuracy for simple slot shapes, while generally avoiding substantial damage to surrounding components and materials. Also, it is capable of cutting openings in various substrates having different materials without the generation of excessive heat. Furthermore, it allows for improved relative placement accuracies during the production process.
While sand slotting affords these apparent benefits, sand slotting is also disadvantageous in that it may cause microcracks in the semiconductor substrate that significantly reduce the substrate's fracture strength, resulting in significant yield loss due to cracked die. Low fracture strength also limits substrate length which in turn adversely impacts print swath height and overall print speed. In addition, sand slotting typically causes chips to the substrate on both the input and output side of the slot. Normally the chipping is tens of microns large and limits how close the firing chamber can be placed to the edge of the slot. Occasionally the chipping is larger and causes yield loss in the manufacturing process. The chipping problem is more prevalent as the desired slot length increases and the desired slot width decreases.
Feed slots may also be formed by wet chemical etching with, for example, alkaline etchants. Such etching techniques result in etch angles that cause a very wide backside slot opening. The wide backside opening limits how small a particular die on the wafer could be and therefore limits the number of die per wafer (the separation ratio). It is desired to maximize the separation ratio.